Summary: The Mechanism of Virus-Host Interactions Training Grant is a multidisciplinary training program designed to train and educate pre-doctoral and post-doctoral trainees in the broad discipline of Virology. This proposal requests continued support for years 21-25 of the Virology Training Program. The faculty is derived from the Icahn School of Medicine at Mount Sinai (ISMMS) with Dr. Tortorella as the Program Director and Dr. Peter Palese as the Co-Program Director. The research training emphasis is directed toward teaching pre-doctoral and post-doctoral trainees the theory and experimental approaches required for independent scientific investigations. Trainees learn the molecular mechanisms involved in virus replication and host responses to viral infections. Research training areas also include novel approaches for antiviral strategies and vaccine development against medically relevant viruses. Our trainees are highly successful in attaining independent research positions, peer-reviewed publications, and extramural research funding. Accordingly, four pre- doctoral and three post-doctoral positions are requested. The specific aim of the program is to recruit and provide rigorous training to high caliber students and fellows. The continued support of this program will aid trainees in all phases of their development including understanding scientific method, interpretation of results, presentation of data and conclusions, research ethics, and career guidance. By combining the strengths of an outstanding group of virologists, we have created a world-class virology Training Program. This program is built upon existing collaborations, including research grants, and joint publications between faculty members at ISMMS. The program faculty consists of twenty outstanding virologists who use a diverse array of experimental strategies to study the molecular, cellular, biochemical and immunological interactions of viruses with their hosts.